The present invention is directed primarily to a waste water treatment and recycling system for an electroplating line.
In an electroplating system, the object thereof is to deposit a thin coating of some metal, through electrolytic deposition, onto a substrate. Such a system may include a number of stations, such as cleaning, etching, and multi-layer coating by sequential plating. Since each such station involves the chemical treating of the substrate, whether by batch or continuous treating, a rinse tank follows each chemical treatment to minimize contamination of a subsequent station. Because of solution dragout, each rinse tank in time becomes increasingly contaminated itself. This is particularly critical in the metal plating stations where the contaminants are considered toxic wastes. Present state and federal laws impose severe restrictions on the handling and disposal of such wastes.
A simple system includes a cleaning station to remove such soils as buffing compounds, stamping or cutting lubricants and the like; and acid station dip to remove metal oxides, often called pickling; and finally, electroplating station(s) with one or more metals, such as nickel and gold. The latter combination is particularly suitable in the manufacture of electrical terminals. Gold, for example, is characterized by good electrical conductivity and little or no formation of oxides that can reduce conductivity.
The metal plating step(s) may include, by way of example, immersion of the electrical terminal substrate into a solution (plating bath) of the salt of the metal substrate which is to be plated and is employed as the cathode, or by passing the product, such as part of a continuous strip, over the metal plating bath where the solution thereof is pumped up to engulf, i.e. achieve a fountain effect, then return to the plating tank. The anode of the system may be of the same metal which is to be coated or may be a conductor which is chemically unaffected by the electroplating reaction, A low-voltage current is then passed through the solution, electrolyzing and plating the cathodic substrate with the metal in the solution. When the coating on the object is of the desired thickness, the substrate is removed and passed to a rinse tank where the residual plating solution is removed from the plated objects, such as by the aid of air knives critically disposed at the exit end of such tank. Actually, the use of air knives is well known, and may typically be found at each tank of the plating system to minimize dragout therefrom.
After a period of operation, it will be understood that contaminates are being dragged out of the plating solution into such rinse tank, resulting in a buildup therein of contaminants. It is important to maintain the rinse solution below a certain level of concentration in order to maintain an effective rinse operation and to prevent spotting or other deterioration in the quality of the plated substrate. While fresh water can be added to the rinse tank to dilute and maintain an appropriate contaminant level, problems of disposal arise on the solution withdrawn from the tank.
Various proposals have been offered by the prior art for treating the waste rinse water in plating systems. Such prior art systems include U.S. Pat. No. 4,781,806 to Tenace, wherein there is taught a system in which water use efficiency is achieved by means of limited use of overhead water sprays, multiple rinse tank backflow to the prior process tank and water evaporation from said process tanks. In addition, all waste water not returned to the prior process tank locally at each plating subassembly is transferred to an in-plant sump for common evaporative treatment.
Other prior art systems are disclosed in U.S. Pat. No. 3,616,437 to Yagishita, and U.S. Pat. No. 3,637,467 to Spatz. The former system is directed to a system for reclaiming plating wastes wherein a liquid rinse water is brought into a tower where it is heated by steam in order to partially vaporize it. The vapor is then passed to an ejector where it is introduced into cooling water to be condensed and then brought to a reservoir.
Spatz, the latter development, relates to a metal reclamation process and system which uses a primary rinse tank and a secondary rinse tank. Liquid is drawn off through a conduit and passed to a pump where it is brought into a reverse osmosis unit, the concentrate of which passes back to the plating tank and wherein permeate is brought through a conduit back to the primary rinse tank.
The present invention, in contrast to the above, teaches a simple system which is fully recyclable, that is, does not create any waste product.